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setup_bridgenetfiltering.go
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setup_bridgenetfiltering.go
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//go:build linux
package bridge
import (
"context"
"errors"
"fmt"
"os"
"syscall"
"github.com/containerd/log"
)
// setupIPv4BridgeNetFiltering checks whether IPv4 forwarding is enabled and, if
// it is, sets kernel param "bridge-nf-call-iptables=1" so that packets traversing
// the bridge are filtered.
func setupIPv4BridgeNetFiltering(*networkConfiguration, *bridgeInterface) error {
if enabled, err := getKernelBoolParam("/proc/sys/net/ipv4/ip_forward"); err != nil {
log.G(context.TODO()).Warnf("failed to check IPv4 forwarding: %v", err)
return nil
} else if enabled {
return enableBridgeNetFiltering("/proc/sys/net/bridge/bridge-nf-call-iptables")
}
return nil
}
// setupIPv6BridgeNetFiltering checks whether IPv6 forwarding is enabled for the
// bridge and, if it is, sets kernel param "bridge-nf-call-ip6tables=1" so that
// packets traversing the bridge are filtered.
func setupIPv6BridgeNetFiltering(config *networkConfiguration, _ *bridgeInterface) error {
if !config.EnableIPv6 {
return nil
}
if config.BridgeName == "" {
return fmt.Errorf("unable to check IPv6 forwarding, no bridge name specified")
}
if enabled, err := getKernelBoolParam("/proc/sys/net/ipv6/conf/" + config.BridgeName + "/forwarding"); err != nil {
log.G(context.TODO()).Warnf("failed to check IPv6 forwarding: %v", err)
return nil
} else if enabled {
return enableBridgeNetFiltering("/proc/sys/net/bridge/bridge-nf-call-ip6tables")
}
return nil
}
// Enable bridge net filtering if not already enabled. See github issue #11404
func enableBridgeNetFiltering(nfParam string) error {
enabled, err := getKernelBoolParam(nfParam)
if err != nil {
var pathErr *os.PathError
if errors.As(err, &pathErr) && errors.Is(pathErr, syscall.ENOENT) {
if isRunningInContainer() {
log.G(context.TODO()).WithError(err).Warnf("running inside docker container, ignoring missing kernel params")
return nil
}
err = errors.New("ensure that the br_netfilter kernel module is loaded")
}
return fmt.Errorf("cannot restrict inter-container communication: %v", err)
}
if !enabled {
return os.WriteFile(nfParam, []byte{'1', '\n'}, 0o644)
}
return nil
}
// Gets the value of the kernel parameters located at the given path
func getKernelBoolParam(path string) (bool, error) {
line, err := os.ReadFile(path)
if err != nil {
return false, err
}
return len(line) > 0 && line[0] == '1', nil
}
func isRunningInContainer() bool {
_, err := os.Stat("/.dockerenv")
return !os.IsNotExist(err)
}